In the electrolytic printing art there are at least two general schemes for printing processes. In one such scheme, metallic ions from one of the electrodes are introduced into the printing sheet, and they are either combined with colorless materials already present in the printing sheet in order to form colored complexes or are precipitated as fine metallic particles.
A disadvantage of the above discussed consumable scheme is the fact that the stylus is consumed in the process. This requires complicated printed mechanisms with feeding devices to keep the stylus working.
In another scheme, the electrodes are not consumed, and the writing is accomplished by the electrolytic modification of materials already in the printing sheet. An example of such a procedure is one which employs the reaction of starch and iodine to effect writing. Generally, in this scheme, the electrolysis of potassium iodide or another iodide compound in the paper generates free iodine which reacts with the starch which is also present in the paper, thereby producing a purple starch-iodide complex.
Another example of such a scheme includes a dry electrolytic printing in which a very special paper is used consisting of one or two metallized layers. Inherent in this scheme are the disadvantages of requiring expensive paper, requiring special layers of materials, and the requirement of voltages that exceed 100 volts for printing.
The nonconsumable schemes, such as the starch-iodine method, suffer from the lack of permanency of the printing due to fading of the printed works and also the discoloration of the paper upon storage.